This invention relates to an integrating phase discriminator which is disposed on a power system to protect system equipment.
A conventional phase discriminator circuit of the type referred to has comprised: a pair of rectangular waveshaping circuits for respectively converting a first and a second AC input to corresponding rectangular waveforms; an adder circuit for adding the converted rectangular waveforms together to form the sum thereof; a full-wave rectifier circuit for full-wave rectifying the sum from adder circuit; a zero shifting circuit for shifting a zero level of an output voltage from the full-wave rectifier circuit; an integration circuit for integrating the zero shifted voltage; a level detector circuit which is responsive to an integrated voltage in excess of an operation detecting level from the integration circuit for delivering an operating signal and which is also responsive to an integrated voltage which is less than a reset detecting level for delivering an inoperative signal; and a control circuit for deciding whether an output from the level detector circuit is the operating or inoperating signal. When the output from the level detector circuit is the inoperative signal, as decided thereby, the control circuit delivers an operating signal. On the detector circuit other hand, when that output is the operating signal, as decided thereby, the control circuit delivers a resetting signal.
The phase discriminator circuit as described above has determined the phase relationship between the first and second AC inputs so that the inoperative signal is delivered when the phase difference is not less than 90 degrees between the two AC inputs and the operative signal is delivered when the phase difference is less than 90 degrees.
Conventional integrating phase discriminator circuits such as described above have been disadvantageous in that, with the phase difference between the two AC inputs approximating 90 degrees, operation and reset sensing times are delayed.
Accordingly, it is an object of the present invention to provide a new and improved phase discriminator circuit which operates and resets fast and which has means for preventing the operation and reset setting from being delayed.